According to an ink jet system described in U.S. Pat. No. 4,723,129 or U.S. Pat. No. 4,740,796, recording with a high density and a high definition and of a high quality can be conducted at a high speed. According to this ink jet system, color recording can be attained. The recording head in this ink jet system can be prepared utilizing the techniques in the field of semiconductor. The apparatus can be, therefore, relatively easily miniaturized.
In such an ink jet system, an ink jet head provided with a plurality of ink discharging outlets of an extremely minute size is used. Upon conducting recording using such ink jet head, ink is discharged through the ink discharging outlets upon the application of a recording signal to spatter and deposit on a record medium, thereby achieving the recording.
The conventional ink jet head is either of the so-called continuous type in which ink is continuously discharged such that the ink is selectively deposited on a record medium or of the so-called on-demand type in which only droplets of ink necessary for recording are intermittently discharged to a record medium.
As for the on-demand type ink jet head, there are typically known a full-line type ink jet head in which a plurality of ink discharging outlets are arranged to correspond to the width of a record medium, and a serial scanning type ink jet head in which recording is conducted by moving the head in ralation to a record medium.
Incidentally, as for an ink jet apparatus in which such an ink jet head as above described, there are still such shortcomings to be solved as will be described in the following. That is, in the case of conducting recording by using an ink jet head provided with a plurality of discharging outlets of a minute size through which ink is discharged in fine-grained form, dirts or dusts present in the recording apparatus, paper powder resulted from a record medium, or droplets of ink are likely to deposit on a discharging outlet face 1a provided with discharging outlets 1b or at positions in the vicinity of the discharging outlets as shown in FIGS. 7(a) and 7(b). These deposits often hinder the direction of flight of droplets discharged from the discharging outlets, or they are sometimes dried and solidified to plug up some of the discharging outlets such that ink cannot be not discharged through those discharging outlets.
In order to eliminate these problems, there has been proposed a so-called blade cleaning method wherein the discharging outlet face deposited with such foreign matters is brushed by means of a blade made of an elastic material such as polyurethane rubber, polyester-urethane rubber, hydrogenated nitrile rubber, or silicone rubber to remove the foreign matters from the discharging outlet face.
Now, there is an increasing demand not only for a mono-color ink jet recording apparatus but also for a multi-color ink jet recording apparatus provided with four individual ink jet heads respectively capable of discharging ink of a different color of yellow, magenta, cyanogen, or black. In the case of the recording in which color tone is varied using these four inks of a different color, it is necessary to discharge a plurality of different inks as for a dot and because of this, rather strict discharging accuracy is required than that in the case of conducting recording using a momo-color ink jet recording apparatus. Therefore, it is necessary for the discharging outlet face of each of the recording heads, which discharge individual ink of a different color, to be maintained in a cleaned state so that stable ink discharging is always provided. For this purpose, the cleaning reliability by means of the blade cleaning is necessary to be always secured.
As for the cleaning blade used in such full-color recording apparatus, there are known a configuration in which an independent cleaning blade is installed in each of the recording heads and another configuration in which a common cleaning blade is installed in the apparatus so that each of the recording heads can be cleaned by the common cleaning blade. In the viewpoint of reducing the area occupied by the cleaning blade in the recording apparatus as much as possible in order to miniaturize the size of the recording apparatus, the manner of cleaning each of the four recording heads by a common cleaning blade is the most desirable. However, in this cleaning manner of cleaning the individual recording heads continuously discharging different inks by a common cleaning blade, there is a tendency that those different inks are mixed on the cleaning blade to result in causing the formation of an image defective in color tone.
In order to eliminate this problem, there has been proposed a manner in which the cleaning is conducted successively from the recording head of discharging ink of relatively light color to the recording head of discharging ink of dark color to prevent occurrence of ink admixture at the recording head of discharging light color ink.
Another manner has been proposed in which an ink absorbent is disposed between each adjacent color ink jet heads, after one of the heads has been cleaned by a cleaning blade, ink deposited on the cleaning blade is removed by the ink absorbent, wherein the next head can be cleaned by the cleaning blade without suffering from any negative influence from the previously cleaned head.
In the following, description will be made of the latter cleaning manner with reference to FIG. 1. As apparent in FIG. 1, a main scanning carriage 2 provided with ink jet heads 2 is designed to travel on a main scanning rail 3. In the non-recording zone separate from the recording zone in the apparatus, a cleaning blade 4 is arranged such that it contacts with a discharging outlet face 1a of the ink jet head 1. Reference numeral 5 indicates a holder which serves to fix the cleaning blade 4. By moving the main scanning carriage 2 in the direction expressed by mark A, the discharging outlet face 1a is rubbed by the cleaning blade 4 arranged in the non-recording zone, whereby deposits X such as ink droplets, paper powder, dusts, and the like which are deposited on the discharging outlet face 1a are removed by the action of an edge of the cleaning blade 4. The ink deposited on the cleaning blade 4 is removed by an ink absorbent 6 which is disposed between each adjacent ink jet heads. Thus, the cleaning blade 4 in cleaned state comes to the result of serving to clean the next ink jet head. According to this manner, all the individual recording heads of discharging ink of a different color can desirably be cleaned by the cleaning blade in cleaned state without causing admixture among the different inks. In this cleaning manner, the cleaning blade is rubbed with the discharging outlet face as many times as the number of the ink jet heads in one cleaning operation cycle and therefore, the frequency of the cleaning blade to be rubbed is greater than that in other cleaning manner.
Independently, in recent years, research and development have been made not only of high speed recording but also of the manner which enables high-volume recording by a single recording apparatus comprising an ink jet recording head of the head-exchangeable type in such viewpoints as will be described in the following.
For instance, in the case of the high speed ink jet recording apparatus, since the amount of ink to be discharged in terms of unit hour unavoidable becomes great, ink becomes more liable to deposit on the discharging outlet face of the recording head. In order to avoid occurrence of this problem, it is necessary to shorten the timing of the cleaning of the recording head and to frequently conduct the cleaning.
In the case of the ink jet recording apparatus which enables high-volume recording, when the apparatus is repeatedly used over a long period of time while exchanging the recording head many times, the frequency of using the cleaning blade in order to clean those recording heads unavoidably becomes extremely great.
Thus, it is understood that the cleaning operation cycle in such ink jet recording apparatus as above described is repeated great many times. Particularly, in the case of the foregoing color recording, as described in the above with reference to FIG. 1, since the cleaning blade is rubbed not only with the discharging outlet face of the recording head but also with the ink absorbent, the frequency of the cleaning blade to be rubbed becomes significantly great. In view of this, it is desired for the cleaning blade to be further improved in terms of durability.
Now, there are known various cleaning blades to be used in the blade cleaning method which are constituted by an elastic material such as silicone rubber, hydrogenated nitrile rubber, polyester-urethane rubber, or polyether-urethane rubber.
However, any of these materials has problems such as will be under described.
That is, silicone rubber is relatively poor in abrasion resistance. Because of this, when rubbed continuously with the ink jet head and the ink absorbent, the silicone rubber member is gradually worn and as a result, the cleaning which is conducted utilizing an edge portion of the cleaning blade becomes insufficient. Particularly problems are occurred in this case in that the worn cleaning blade permits ink to pass through its portion in contact with the discharging outlet face of the head, wherein foreign matters deposited cannot be sufficiently removed. This leads to causing problems such that the residual ink or foreign matters left without having been removed prevent ink from being stably discharged through the discharging outlets, wherein stable flight orbit of ink particle cannot be attained, resulting in providing defective recorded images accompanied by blurred portions or lines or that the discharging outlets of the ink jet head are clogged with powdery materials generated when the cleaning blade is worn, resulting in providing defective recorded images accompanied by lines. Other than these problems, there is also a problem in that inorganic fillers such as silica contained in the silicone rubber sometime damage portions near the discharging outlets of the ink jet head upon conducting the cleaning by the cleaning blade, resulting in preventing ink from being stably discharged while providing flight orbit of ink particle as desired, wherein defective recorded images are provided. Further, oily components contained in the silicone rubber are liable to modify the composition of ink, wherein the ink is hardly bubbled, resulting in providing defective recorded images accompanied by undischarged lines caused due to insufficient ink bubbling.
In the case where the silicone rubber cleaning blade is employed for cleaning an ink jet system in which droplets of ink are discharged through a discharging element utilizing thermal energy, the foregoing oily components of the silicone rubber are liable to enter into the discharging outlets, wherein the heat generating body, which serves to generate thermal energy, is liable to be sintered because of those oily components, resulting in preventing ink from being discharged, and as a result, there cannot be obtained desirable recorded images.
The hydrogenated nitrile rubber is relatively poor in abrasion resistance as well as the silicone rubber. In the case where the cleaning blade constituted by the hydrogenated nitrile rubber is employed for cleaning the foregoing color ink jet recording apparatus provided with the ink absorbents, significant wear is caused at the cleaning blade when continuously used over a long period of time as a result of having been repeatedly rubbed with the ink jet heads and the ink absorbents, wherein the cleaning cannot be sufficiently conducted, resulting in leaving ink deposits or other deposited foreign matters without being removed and a result, desirable ink discharging accuracy cannot be attained, resulting in providing defective recorded images. Because of this, the cleaning blade constituted by the hydrogenated nitrile rubber is problematic especially in terms of durability. The hydrogenated nitrile rubber usually contains oily components for the purpose of improving its hardness. These oily components are liable to enter into the recording heads, wherein there are problems such that their heat generating body is liable to be sintered because of the oily components or the composition of ink is liable to be modified as well as in the case of using the silicone rubber.
Now, urethane rubbers such as polyester-urethane rubber and polyether-urethane rubber are presently often used as a constituent material of the cleaning blade since they are not necessary to be incorporated with either an inorganic filler or an oily component, and they are free of the foregoing problem of damaging the discharging outlet face due to the filler and of the foregoing problems due to the oily components, and are relatively satisfactory in therms of durability when used as the cleaning blade.
However, in the case where the cleaning blade constituted by such urethane rubber is employed for cleaning the full-color ink jet apparatus shown in FIG. 1, there is a problem in that when the cleaning blade continuously and repeatedly rubbed with the four ink jet heads and ink absorbents, such partially worn portions as shown in FIG. 4(b) are liable to occur at the edge portion of the cleaning blade to provide an unevenly worn state (a face state provided with irregularities). With the cleaning blade having such unevenly worn state at the edge portion, satisfactory cleaning cannot be attained in the cleaning operation, wherein ink-escape 10B is caused through such partially worn portion as shown in FIG. 7(d), resulting in leaving ink deposits in the vicinity of the discharging outlets without being removed. Such residual ink deposits in the vicinity of the discharging outlets is apt to cause so-called gap defect wherein flight orbit of ink discharged from the discharging outlets is deranged. Further, in the case where the unevenly worn state is enlarged and the amount of such ink deposits left without being removed is increased, ink discharged is sometimes taken into the ink deposits, resulting in causing a situation such that ink is not discharged, that is, no image is recorded. In addition, in the case where an unevenly worn state is occurred at the edge portion of the cleaning blade, the urging pressure by the cleaning blade is centralized at other edge portion thereof with no broken portion and as a result, the area to be contacted with ink (that is, meniscus portion) is increased, resulting in promoting the situation of pulling out ink from the discharging outlets (see, FIG. 5(b)).
Particularly, as for polyester-urethane rubber, it is liable to cause hydrolysis because of its structure and thus, it is liable to deteriorate due to moisture of the air. In the case where the cleaning blade constituted by this rubber is used in an ink jet recording apparatus in which aqueous ink is used, there is a fear that the rubber is deteriorated due to moisture of the ink to lose its elasticity, resulting in not providing a desired urging force to the edge portion of the cleaning blade upon conducting the cleaning operation. Thus, the cleaning blade is poor in durability upon repeated use over a long period of time.
The foregoing urethane rubbers have at least a polar group in their structure. Because of this, as for the cleaning blade constituted by such urethane rubber, the constituent urethane rubber is liable to absorb aqueous ink used in an ink jet recording head. Particularly, the cleaning blade is continuously contacted with such ink over a long period of time, the constituent urethane rubber becomes dwelled because of the ink. This situation results in causing various problems. That is, the cleaning blade pulls out ink in the discharging outlets by virtue of the affinity upon conducting the cleaning (see, FIG. 5(b)), wherein ink remains in the vicinity of the discharging outlets without being removed. Such residual ink affects the direction of ink discharged to deteriorate the discharging accuracy, wherein the foregoing gap defect is caused. Other than this, the residual ink remained on the cleaning blade often becomes such that it is hardly removed after the cleaning and thus, it is remained as a blade foul which leads to reducing the cleaning efficiency in successive cleaning operation. Especially, in the case where the cleaning blade is used in an ink jet recording apparatus in which a plurality of inks having a different color are used, off-shade is often occurred due to such deterioration in discharging accuracy. In addition to this, at the stage where the residual ink taken up by the cleaning blade is removed by the ink absorbent, when the cleaning blade has a strong affinity with the ink, sufficient removal of the ink cannot be attained, resulting in causing undesirable color mixture.
The above problems relating to the cleaning blades are not so serious, for example, in the case of a personal type ink jet recording apparatus in which the number of recording sheets used per recording is not large and which is not frequently used. Particularly, as for the personal type ink jet recording apparatus, it is usually of a system in which recording is conducted with one ink, and the number of recording sheets used per recording is small and in addition, it is usually not used such that the cleaning is necessary to be frequently conducted.
On the other hand, in the foregoing full-color type recording apparatus, high speed recording apparatus or long-time usable recording apparatus of the recording head exchangeable type, the use frequency of the cleaning blade is higher than that in the case of using of the personal type recording apparatus in view of restoring or improving the quality of an image recorded, and a high reliability and durability are required for the cleaning blade. Particularly in the case of the full-color recording apparatus, as above described, since the cleaning blade is continuously rubbed with a plurality of recording heads and a plurality of ink absorbents in one cleaning operation, and the frequency of the cleaning blade to be rubbed with the recording heads and the ink absorbents is extremely increased, and therefore, the cleaning blade is required to be satisfactory in terms of reliability and durability.
Under such circumstance as above described, the present invention is intended to provide a material suitably usable as the cleaning blade for the recording head which is installed in a recording apparatus for which provision of a high quality recorded image is required and which is continuously used over a long period of time.
The present inventors made various studies in order to eliminate the foregoing problems in the prior art. The studies by the present inventors were conducted while focusing on the polyurethane rubber materials above illustrated as the constituent material of the cleaning blade, in the viewpoints that the polyurethane rubber materials are not necessary to be incorporated with inorganic fillers or/and oily components which are apt to give negative influences not only to ink but also to the recording head as above described, and they are relatively good in abrasion resistance. The present inventors conducted various experimental studies with respect to these polyurethane materials while selecting their constituent material, and changing and adjusting an additive to be incorporated. As a result, there were obtained such knowledges as will be described in the following.
Firstly, description will be made of the knowledges obtained with respect to improvement in abrasion resistance of the cleaning blade. In general, as the curing agent for polyurethane rubber, there are used a bifunctional component as a chain-lengthening agent and a polyfunctional (which means trifunctional or more) component as a cross-linking agent are used. The polyfunctional component serves to prevent occurrence of slide, deviation or the like among adjacent molecules when the rubber is applied with a deformation stress. This makes it possible to form a rubber which is free of permanent deformation and which is small in pressure permanent distortion. However, the polyfunctional component constrains movements of the adjacent molecules not only to prevent the polar groups in the urethane rubber from being mutually reacted (agglomeration) but also to prevent the backbone chain molecules in the urethane rubber from being mutually reacted (crystallization). This results in reducing the strength (tear propagation strength and tensile yield strength) of the rubber. Especially, in the case of polyether-urethane rubber, a distinct difference is provided with respect to tear propagation strength and tensile yield strength depending upon whether the polyfunctional component is present or not present.
The results obtained as a result of the studies by the present inventors showed that the state of being worn differs depending upon whether a polyfunctional component is present or not present. Particularly, the present inventors studied of abrasion by providing a cleaning blade comprised of a polyether-urethane rubber with a composition containing a polyfunctional component, setting the cleaning blade to an ink jet recording apparatus of the constitution shown in FIG. 8, and operating the apparatus. As a result, such partially worn portions (chippings) as shown FIG. 4(b) were occurred at the cleaning blade to have been rubbed with the discharging outlet face of the recording head, those worn portions of the cleaning blade being in unevenly worn state. The same procedures have been repeated, except that a cleaning blade comprised of a polyether-urethane rubber containing only a bifunctional component was used. The results showed that the cleaning blade has such a uniformly worn face as shown in FIG. 4(a) with no accompaniment of such partially worn portions.
This difference in terms of worn state is serious as for the cleaning blade for the ink jet recording head. That is, in the case where an unevenly worn state due to such chippings as shown in FIG. 4(b) is occurred at the cleaning blade, upon conducting the cleaning operation, ink-escape 10B is caused through such partially worn portions as shown in FIG. 7(d) to remain ink in the vicinity of the discharging outlets, wherein such residual ink leads to causing defects in the recording such as gap defect or non-discharging wherein no recorded image is provided. In addition, in the case where such partially worn portions are occurred at the edge portion of the cleaning blade, the urging pressure by the cleaning blade is centralized at other edge portion thereof with no accompaniment of such partially worn portion, resulting in promoting the situation of pulling out ink from the discharging outlets (see, FIG. 5(d)).
On the other hand, in the case of using the cleaning blade comprised of the bifunctional component-containing polyether-urethane rubber, the cleaning blade is rubbed to provide a uniformly worn face at the edge portion with no accompaniment of such partially worn portions. Therefore, no ink-escape is occurred, and a uniform urging force is provided by the cleaning blade, wherein the amount of ink to be pulled out from the discharging outlets can be minimized, and the cleaning can be conducted in good state as shown in FIG. 7(c).
Herein, description will be made of the situation wherein ink is pulled out from the discharging outlets with reference to FIGS. 2 and 3.
A cleaning blade 7 which serves to rub the ink discharging outlet face 1a of the recording head is pressed at a relevant pressure. Therefore, if the cleaning blade 4 is accompanied by such broken portions as above described at the edge portion thereof, a stress is centralized at other edge portion thereof with no partially worn portion. In this case, there is a tendency that the edge portion with no partially worn portion of the cleaning blade 4 enters into the inside of an ink discharging outlet 1b in such a state as shown in FIG. 2. Incidentally, at the ink discharging outlet 1b, there is formed a meniscus M due to a given surface tension possessed by the ink present in the ink pathway and a negative pressure applied to the ink.
When the edge portion of the cleaning blade 4 at which the stress is centralized enters into the inside of the ink discharging outlet as above described, the edge portion occasionally contacts with the meniscus portion M according to the entrance extent of the edge portion. If the cleaning blade is moved under the state thus contacted, the ink in contact with the cleaning blade is eventually pulled out from the discharging outlet (see, FIG. 5(b)). Herein, the residual ink present between the cleaning blade 4 and the discharging outlet 1a of the recording head indicates the ink taken up by the cleaning operation.
On the other hand, in the case of the cleaning blade comprised of the polyether-urethane rubber containing a bifunctional component only as the curing agent, since no broken portion is occurred at the edge portion thereof and no stress centralization is occurred, such a phenomenon that the edge portion of the cleaning blade enters into the inside of the discharging outlet 1b of the recording head is hardly occurred. If the edge portion of the cleaning blade should enter into the inside of the discharging outlet of the recording head, the entrance extent is extremely small, wherein there is a slight occasion for the edge portion to be contacted with the meniscus M. In addition, in the case of using the cleaning blade comprised of the polyether-urethane rubber containing a bifunctional component only as the curing agent, a uniformly worn state is provided at the edge portion thereof. Therefore, as shown in FIG. 3, if the cleaning blade should be worn, the edge portion of the cleaning blade hardly enters into the inside of the discharging outlet 1b of the recording head. If the abraded edge portion of the cleaning blade should enter into the inside of the discharging outlet of the recording head, the entrance extent is extremely small, wherein there is a slight occasion for the edge portion to be contacted with the meniscus M. This means that ink is hardly pulled out from the discharging outlet upon conducting the cleaning operation.
Other than the above knowledges, the present inventors obtained the following knowledges in view of necessity of improving the water repellency of the cleaning blade.
The phenomenon shown in FIG. 2 in which during the cleaning operation, the cleaning blade 4 enters into the inside of the discharging outlet 1b of the recording head and it contacts with the meniscus M of ink formed in the discharging outlet to pull out the ink deposited on the cleaning blade from the discharging outlet along with the movement of the cleaning blade (wherein the amount of the ink to be pulled out is different depending upon the self surface tension of the ink and the water repellency of the cleaning blade) differs also depending upon the water repellency of the cleaning blade.
Shown in FIG. 6 is of the interrelation between the angle at which the cleaning blade material and the area of the ink deposited. As apparent from FIG. 6, it is understood that there is a tendency that the smaller the angle .theta. at which cleaning blade material is contacted, the greater the area of the ink deposited, and the greater the angle .theta. at which cleaning blade material is contacted, the smaller the area of the ink deposited. Particularly, the angle at which the cleaning blade 4 is contacted with the ink at the position where the cleaning blade is in contact with the discharging outlet is related to the amount of the ink to be pulled out, wherein the lower the water repellency of the cleaning blade, the smaller the foregoing ink contact angle, resulting in increasing the amount of the ink deposited on the cleaning blade, whereby the amount of the ink to be pulled out is increased. Therefore, at the conditions under which ink is liable to deposit on the constituent material of the cleaning blade, the ink once deposited on the cleaning blade at a given position thereof comes to a result that it is taken out from the discharging outlet without being removed along the movement of the cleaning blade during the cleaning operation (see, FIG. 5(b)).
The present inventors obtained a finding that the angle at which the cleaning blade is contacted with the ink can be enlarged by imparting an relevant water repellency to the cleaning blade and by this, the amount of the ink deposited on the cleaning blade can be diminished, whereby the amount of the ink to be pulled out from the discharging outlet can be reduced, and the cleaning can be desirably conducted.